Bleaching chemical pulp



Patented Feb. 16,1937- UNl-TED STATES nmscnmo, cnsmcar. rm

Wilhelm rammed, Berkeley, Calif we. to Great Western Electro-Ohemlcal Company, a corporation of California No Drawing. Application September 21, use, Serial No. 101,791

5 Claims.

This invention relates to the trea ment of chemical wood pulps, particularly kraft, soda and sulphite pulps. I have found that chemical wood pulps can be effectively lightened in color by the addition of salts of sulphoxylic acid. The principal representatives of these compounds are given in the following:

Sodium formaldehyde sulphoxylate NaHSOg-OIhO Zinc formaldehyde sulphoxylate ZnSOs-OHzO BOCHIOHO Zinc formaldehyde sulphoxylsto Zn SOCHrOHO Chemical pulps, when ready for the bleaching operation, usually have a pH very close to that of an alkaline condition, sulphite pulp normally running about 6.5 and kraft and soda Dulps between 6.8 and 7.5. I have found, for example, upon adding a sulphoxylate to a kraft pulp, that the pulp turns black upon addition of the sulphoxylate. I have found that a satisfactory bleaching operation can be secured if the pH of the pulp is adjusted in any suitable manner, as by addition of a suitable alkali, an alkaline salt, an acid or an acid salt, so that the pH is in the neighborhood of 5, and preferably between 4 and '7. As suitable acidifying agents I have effectively utilized sodium acid sulphate, sodium acid phosphate, sodium bisulphite, sulphite cooking liquor, sulphur dioxide or sulphurous acid or an acid as sulphuric acid while as alkaline materials I can use soda ash, borax, lime and the like.

These are effective in small amounts, usually from 0.25% to 3% (on an air dry pulp basis) suillcing.

As suitable compounds which I can use, I mention sulphoxylates containing an aldehyde or a ketone in combination, or any other aldehyde, such as acetaldehyde, or any ketone, such as acetone or other ketone, while the metal sodium can be replaced by zinc, potassium, magnesium or by the ammonium radical. The outstanding characteristics of these compounds are that they are stable at ordinary temperature and that their bleaching effect is exerted between about F. and 212 F.

In utilizing the process oi my invention, I either add the compound as a solid, in form of a solution to the material to be bleached, or else I form the compound in situ in the material undergoing bleaching. Thus I have bleached pulp by adding to the hot pulp at about 180 F. zinc formaldehyde sulphoxylate in small amounts. The pulp reduced quickly in color and finished with a considerably lighter and more permanent color than one bleached under similar conditions with reducing bleaches. I have also successfully bleached pulp by forming the sulphoxylate directly therein by methods well known for manufacture of this material.

Zinc formaldehyde sulphoxylate can be produced readily from zinc hydrosulphite and formaldehyde by the addition of zinc dust in an acid aqueous medium, or else the addition compound, zinc hydrosulphite formaldehyde, can be treated with zinc dust in an acid aqueous medium. Another method is by treatmg hydrosulphite with formaldehyde in the presence of an alkali or by treating the addition compound zinc hydrosulphite formaldehyde with an alkali such as caustic soda, caustic potash or ammonia.

There are also other combinations possible, such as starting out from alkali sulphites or from sulphur dioxide and treating with zinc dust. thereby forming hydrosulphite as the intermediate product.

In practicing the invention I have successfully brightened a kraft pulp, for example, by adding thereto suilicient sodium acid sulphate to lower the pH to pH 5. The pulp was of a 5% density and for each 100 pounds of the pulp on an air dry basis I added a pound of zinc formaldehyde sulphoxylate. The suspension was hot- F. After ten to fifteen minutes the action was largely over but to ensure complete exhaustion of the sulphoxylate, I permitted the pulp suspension to remain in contact with the reducing bleach for a total of about thirty minutes. The bleach was then drained ofl and the brightened pulp then made into paper.

Instead of an aldehyde a ketone can be used. Both ketones and aldehydes form addition products so that any aldehyde or ketone can be. used. The simplest formula for an aldehyde and a ketone iswhere R is hydrogen for an aldehyde and any organic radical for a ketone wherein a carbon is bonded to the carbon in the formula. Any aldehydic or ketonic compound, aliphatic or cyclic, including carbocyclic as well as heterocyc lc, within these formulas can be used as a basis for forming the sulphoxylate.

I claim:

1. The process of bleaching a chemical wood pulp comprising subjecting said pulp to the action of an organic sulphoxylate selected from the group consisting oi aldehyde and ketone sulphoxylates at a pH substantially between 4 and 7 and at a temperature between 100 and 212' I".

2. The process of bleaching a chemical wood pulp comprising subjecting said pulp to the action of a salt of sulphoxylic acid and an aldehyde at a pH substantially between 4 and '1 and at a temperature between 100 and 212 F.

3. The process 0i! bleaching a chemical wood pulp comprising subjecting said pulp to the action of a salt of sulphoxylic acid and a ketone at a pH substantially between 4 and 7 and at a temperature between 100' and 212 F.

4. Bleaching a chemical wood pulp at a temperature between 100' and 212 F. and at a pH between 4 and 7 with an addition product of sulphonlic acid and an organic compound 0! the formula- R-O-R I;

where R is any organic radical and R is hydrogen 15 or any organic radical.

WILHEIM HIRSCHKIND. 

